The polyphenylene ethers and processes for their preparation are well known in the art. They are described in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Blanchard et al, U.S. Pat. Nos. 3,219,625 and 3,219,626, all of which are incorporated by reference. Other patents which show the preparation of polyphenylene ethers include Price et al, U.S. Pat. No. 3,382,212 and Kobayshi et al, U.S. Pat. No. 3,455,880 which are also incorporated by reference.
The processes most generally used to produce the polyphenylene ethers involve the self-condensation of a monovalent phenol in the presence of an oxygen-containing gas and a catalyst comprising a metal-amine complex.
These reactions are usually carried out in the presence of an organic solvent and the reaction is ordinarily terminated by removal of the catalyst from the reaction mixture. In the past, this has been done by the use of aqueous solutions of acetic acid, sulfuric acid, chelating agents such as glycine, nitrilotriacetic acid or its sodium salts. Also in Calicchia et al, U.S. Pat. No. 3,783,147, there was disclosed the use of carbon dioxide in an aqueous extraction solution (carbonic acid) for the separation of the copper-amine catalyst residue from a polyphenylene ether polymerization mixture.
The purpose of extraction of polyphenylene ether solutions with CO.sub.2 (aqueous carbonic acid) is to remove both the amine and copper components of the catalyst, but CO.sub.2 is most effective in removing the amine only. Since copper carbonate has limited solubility in water it has a tendancy to precipitate resulting in unacceptably high levels of residual copper in the polyphenylene ether.
The use of ammonia and CO.sub.2 as an extraction agent allows the use of low levels of CO.sub.2 to give effective removal of the copper primarily. The amine is left largely in the organic phase to be recovered with the solvent. Alternately, large amounts of CO.sub.2 may be used with small amounts of ammonia to give more effective removal of copper and still effectively remove the amine. The use of ammonia with CO.sub.2 is therefore an improvement over CO.sub.2 alone in that it provides improved removal of copper.
It has been found that the use of an aqueous carbon dioxide-ammonia extraction feed results in more than an additive effect from the use of ammonia, as the use of aqueous ammonia or aqueous carbon dioxide alone provides a polymer having substantially higher residues of copper than is obtainable when these materials are used in combination.
Accordingly, it is a primary object of this invention to provide an improved process for the separation of a copper-amine catalyst from a polyphenylene ether reaction mixture.
It is also an object of this invention to provide an improved process for the separation of a copper-amine catalyst from a polyphenylene ether reaction that may be carried out in a continuous manner.
It is also an object of this invention to provide an efficient liquid-liquid extraction system to remove copper-amine catalyst residues.